Note that f is continuous on (−∞, 6) and (6, ∞). for the function to be continuous on (−∞, ∞), we need to ensure that as x approaches 6, the left and right limits match. first we find the left limit. lim x→6− f(x) = lim x→6− (cx2 + 7x) = next, we find the right limit. lim x→6+ f(x) = lim x→6+ (x3 − cx)